I realized just now that Arthur knows a couple of commands that aren't in standard wording--he knows "drop it" but he more consistently responds to "yucky!" when he's got something in his mouth he's not supposed to, and he doesn't actually know "stop" at all--you have to say "halt!" It was mostly accidental that he learned these commands (I would say "Yucky, yucky, drop it" when we first got him and I guess it just evolved into "yucky!", and I guess I just said "halt!" so many times that that's what he thinks is the standard command).
I also realized that he knows "where are my slippers?" which is kind of awesome. Considering he's the one who always hides them, it's a pretty useful command.
What fun commands do your dogs know?